It is known in the art that high yield catalytic components of Ziegler-Natta type may be obtained by contacting a titanium compound comprising at least a titanium-halogen bond with a solid support comprising a magnesium halide. Solid catalytic components of the Ziegler-Natta type are obtained, for instance, by reacting TiCl4 with a support containing a magnesium compound that can be a magnesium dihalide, such as MgCl2, or an alcoholate or haloalcoholates of magnesium, such as ethoxymagnesiumchloride or diethoxymagnesium. A particular type of support consists of adducts of MgCl2 with aliphatic alcohols, such as ethanol, in the form of spherical particles. It is known that in order to obtain a more effective catalyst component, the titanation of the particles of the solid support should be carried out at a high temperature, generally above 80° C., and preferably in the range 90–130° C. When a supported catalyst is produced for the polymerisation of propylene or higher α-olefins, it is necessary the presence of an internal electron donor compound in the solid catalytic component. In fact, the presence of said electron-donating compound (Di) allows the preparation of supported catalysts endowed not only with a high catalytic activity, but also with a high stereospecifity.
Electron donor compounds suitable for the preparation of solid catalyst components can be selected from esters, ketones, amides and amines. A particular class of suitable internal electron donors is represented by mono- and di-alkyl esters of aromatic carboxylic acids, such as diisobutylphtalate or ethylbenzoate. Besides these compounds, also specific ethers have been proved to be effective as internal donors. EP 361 494 discloses solid catalyst components comprising, as an internal electron-donor, an ether containing two or more ether groups, preferably in 1,3 position, and having specific reaction characteristics towards the anhydrous magnesium chloride and TiCl4. In particular, this ether is capable of forming complexes with activated anhydrous magnesium dichloride in a quantity of less than 60 mmoles per 100 g of MgCl2 and it enters into substitution reactions with TiCl4 for less than 50% by moles. The presence of the above 1,3-diethers in the solid catalytic component causes a remarkable increase of the catalytic activity of the final catalyst, with respect to the case of a conventional electron donor selected from phtalates or ethylbenzoate. Moreover, the catalysts obtained from the reaction of said catalyst component with an Al-alkyl compound exhibit high stereospecifity in the polymerization of olefins, even in the absence of an external electron donor (De). In fact, according to EP 361 494 the use of the above diethers allows to achieve good results in term of activity and stereospecifity even without including an external electron donor compound in the catalyst system.
Another advantage correlated to the presence of a 1,3-diether in the solid catalyst component consists of providing an improved control of the final molecular weight of the obtained polymer, which makes it possible to produce polymers with very high melt flow rates, as those disclosed in EP 622 380. The presence of a 1,3-diether in the solid catalytic component makes more effective use of hydrogen introduced during the polymerization for the regulation of the length of polymeric chains. As a consequence, the use of a 1,3-diether as an electron donor not only makes more flexible the polymerization process itself, but also allows to widen the range of products having a different molecular weight.
EP 728 769 refers to electron donors selected from 1,3-diethers, in which the carbon atom in position 2 belongs to a specific cyclic structure containing at least two unsaturations (cyclopolyenic structure). Said cyclopolyenic 1,3-diethers confer a further increase of the catalyst activity with respect to the ethers heretofore known. Furthermore, the cyclopolyenic 1,3-diethers can be successfully used both as internal and external electron donor compounds.
In view of the above advantages, it is of great technical interest to develop an industrial process for the preparation of a solid catalytic component containing a 1,3-diether as electron donor compound.
According to EP 728 769 a solid catalyst component is obtained by reacting a MgCl2.nROH adduct in the form of spheroidal particles, where n is 1–3 and ROH is preferably an aliphatic alcohol, with an excess of TiCl4 containing a cyclopolyenic 1,3-diether as electron donor. The temperature is initially in the range from 0 to 25° C., and then is increased to 80–135° C. After a time ranging from 30 minutes to 2 hours the reaction product comprising the titanated solid support is separated from the liquid phase. After the separation of the liquid phase, one or more further steps of titanation can be carried out under conditions similar to those described above. After the last reaction with TiCl4, the obtained solid is separated, for example by way of filtration, and washed with a hydrocarbon solvent until no chlorine ions can be detected in the washing liquid. The experiments are carried out in a laboratory reactor, specifically in a 500 ml glass reactor equipped with a filtering barrier. Although the description of the examples is detailed in some aspects, it must be noted that the cited document fails to recognise any criticality in the step of slurry separation. In fact, the conditions under which the separation of the slurry is carried out (time, temperature, stirring) are not reported.
Conversely, the Applicant has found that during the preparation of solid catalyst components containing 1,3-diethers, the control of the parameters of the separation step can have a relevant impact on the properties of the final catalyst. This problem is particularly apparent in the large-scale production, where in view of the large volumes of reactants involved, any failure to control the parameters of the separation step can cause a remarkable worsening of the catalytic properties of entire lots of catalyst components.
The Applicant has now found that in order to prepare solid catalyst components containing 1,3-diethers with high activity and stereospecifity, it is important to select properly the operative conditions both in the titanation step and in the successive separation step of the slurry.
It is therefore an object of the present invention a process for preparing a diether-based catalyst component in which:                a) a slurry is obtained by contacting a solid support comprising a magnesium halide or a precursor thereof, one or more 1,3-diethers and a liquid phase containing a titanium compound, and        b) the obtained slurry is then subjected to a solid/liquid separation step in order to isolate a diether-based catalyst component;said separation step b) being characterized in that the ratio between the solid/liquid separation velocity and the final amount of separated solid must be higher than 0.5 liter/(min·Kg), preferably comprised in the range from 0,7 to 2 liter/(min·Kg). As solid/liquid separation velocity is intended the volume of liquid separated from the solid catalyst component in the unit of time (liter/min).        
The amount of separated solid is intended as the amount of di-ether based catalyst component obtained at the end of step b) and expressed in kg.
The solid/liquid separation step may be carried out according to different separation techniques, such as filtration or centrifugation, preferably by filtration. In this case, the filters are vessels containing one or more filtering units, the openings thereof are comprised between 1 to 200 μm. The differential pressure applied on the filter can range from 50 to 1000 Kpa: in any case, it will be suitably selected in order to get the above mentioned solid/liquid separation velocity. As examples of filters, Nutsche filters (for example the Rosenmund type) can be mentioned: they consist of a tank with a perforated or porous bottom, which may either support a filter medium or act as the filter medium. The filter medium can be a filter cloth, a sintered plate, a porous ceramic structure, a wire screen, or a perforated plate. Also centrifugal-discharge filters, such as a Funda filter, can be used: they consist of a vessel that coassially contains an assembly of horizontal filter plates mounted on a hollow motor-connected shaft. After a suitable filtration time, the rotation of the shaft allows a discharge of the solid deposited onto the filter plates.
In the present invention step a) takes usually place in a reactor situated upstream of the filter. However, both step a) and step b) can also take place in the filter itself.
If step b) is carried out by centrifugation, a rotating drum can be used to separate the slurry. The rotation velocity of the drum must be sufficient to concentrate the solid component as a layer on the walls of the drum, while the liquid can be withdrawn from the central portion of the drum.
In step a) the initial temperature of the liquid phase containing the Ti compound can be in the range from −20° C. to 25° C. Such a temperature is then gradually raised to a value to be kept in the range from 80° C. to 135° C. in order to ensure an effective titanation of the support particles.
A typical scheme for preparing a di-ether based catalyst component according to the present invention is given below.
A vessel provided with stirring means is fed, at a temperature in the range from −20° C. to 25° C., with a liquid phase containing the Ti compound, a 1,3-diether compound and a solid support comprising a Mg halide in the form of spheroidal particles: the molar ratio Mg/1,3-diether is such to be comprised between 0.5 and 50, preferably between 2 and 20;
the temperature of the vessel is then gradually raised to a value comprised between 80° C. and 135° C.; after a residence time comprised between 15 minutes and 3 hours, the obtained slurry is subjected to a solid/liquid separation according to the conditions set in step b);
the above steps a) and step b) can be repeated more times in sequence and finally the separated solid component is washed with a suitable solvent until no chlorine ions can be detected in the washing liquid. The solvent can be a hydrocarbon, such as toluene, pentane, hexane or a halogenated hydrocarbon, such as chloroform.
The process of the invention is of great industrial interest, since the operative conditions selected in steps a) and b) allow the preparation on industrial scale of a diether-based catalyst component able to give a final catalyst characterized by a high level of activity and stereospecifity. Tests carried out by the Applicant and illustrated by the comparative examples below reported, show that when in step b) the ratio between the solid/liquid separation velocity and the final amount of separated solid is less than 0.5 liter/(min·Kg), the worsening of catalyst properties of the final catalyst becomes unacceptable.
The titanium compound to be fed in step a) may be selected from TiCl4, TiCl3 and Ti-haloalcoholates of formula Ti(OR)n-yXy, where n is the valence of titanium, y is a number between 1 and n−1 X is halogen and R is a hydrocarbon radical having from 1 to 10 carbon atoms. The preferred titanium compound is TiCl4.
The solid support to be fed to the vessel in step a) may be a magnesium halide, such as MgCl2, or a Mg compound capable to yield MgCl2 by reaction with a chlorinating agent such as TiCl4.
Particularly preferred supports are adducts of a magnesium halide with an aliphatic alcohol, preferably ethanol. It is preferred that the magnesium halide is in its active form or that the magnesium compound is capable to yield a magnesium halide in its active form when reacted with a chlorinating agent. As it is well known in the field of Ziegler-Natta catalysts, “magnesium chloride in active form” means magnesium chloride characterized by X-ray spectra in which the most intense diffraction line that appears in the spectrum of the non-active halide is diminished in intensity and is replaced by a halo whose maximum intensity is displaced towards lower angles relative to that of the more intense line.
Preferred supports are spheriform adducts of formula MgCl2.pROH, where p is a number between 0,1 and 6 and R is a hydrocarbon radical having 1–18 carbon atoms. Said adducts can be suitably prepared in spherical form by mixing alcohol and magnesium chloride in the presence of an inert hydrocarbon immiscible with the adduct, operating under stirring conditions at the melting temperature of the adduct. Then, the emulsion is quickly quenched, thereby causing the solidification of the adduct in form of spherical particles. Examples of spherical adducts prepared according to this procedure are described in U.S. Pat. No. 4,399,054, U.S. Pat. No. 4,469,648. The so obtained adduct can be optionally subjected to thermal controlled dealcoholation (80–130° C.) so as to obtain an adduct in which the number of moles of alcohol is generally lower than 3 preferably between 0.1 and 2.5. Particularly preferred supports are MgCl2/ethanol adducts with an average diameter in the range from 0.1 to 150 μm, more preferably from 1 to 100 μm.
In a particular embodiment of the present invention, the liquid phase fed to the vessel contains a liquid organic substance having dielectric constant at 20° C. equal to or higher then 2 such as those described in EP-106,141. Preferred liquid organic substances are aromatic hydrocarbons or aromatic halohydrocarbons. The use of aromatic halohydrocarbons, such as chlorinated aromatic hydrocarbons, may lead to superior activities. In the class of non-halogenated hydrocarbons, toluene and ethylbenzene are particularly preferred.
The 1,3-diethers to be fed in step a) show specific reaction characteristics towards the anhydrous magnesium chloride and TiCl4. In particular, these ethers are capable of forming complexes with activated anhydrous magnesium dichloride in a quantity of less than 60 mmoles per 100 g of MgCl2 and enter into substitution reactions with TiCl4 for less than 50% by moles. They have formula (I):
where RI and RII are hydrogen or linear or branched C1–C18 hydrocarbon groups which can also form one or more cyclic structures, with the proviso that RI and RII cannot be contemporaneously hydrogen; RIII groups, equal or different from each other, are hydrogen or C1–C18 hydrocarbon groups; RIV groups equal or different from each other, have the same meaning of RIII except that they cannot be hydrogen; each of RI to RIV groups can contain heteroatoms selected from halogens, N, O, S and Si.
Preferably, RIV is a 1–6 carbon atom alkyl radical and more particularly a methyl while the RIII radicals are preferably hydrogen. Moreover, when RI is methyl, ethyl, propyl, or isopropyl, RII can be ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, isopentyl, 2-ethylhexyl, cyclopentyl, cyclohexyl, methylcyclohexyl, phenyl or benzyl;
when RI is hydrogen, RII can be ethyl, butyl, sec-butyl, tert-butyl, 2-ethylhexyl, cyclohexylethyl, diphenylmethyl, p-chlorophenyl, 1-naphthyl, 1-decahydronaphthyl;
RI and RII can also be the same and can be ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, neopentyl, phenyl, benzyl, cyclohexyl, cyclopentyl.
Specific examples of ethers that can be advantageously used include: 2-(2-ethylhexyl)1,3-dimethoxypropane, 2-isopropyl-1,3-dimethoxypropane, 2-butyl-1,3-dimethoxypropane, 2-sec-butyl-1,3-dimethoxypropane, 2-cyclohexyl-1,3-dimethoxypropane, 2-phenyl-1,3-dimethoxypropane, 2-tert-butyl-1,3-dimethoxypropane, 2-cumyl-1,3-dimethoxypropane, 2-(2-phenylethyl)-1,3-dimethoxypropane, 2-(2-cyclohexylethyl)-1,3-dimethoxypropane, 2-(p-chlorophenyl)-1,3-dimethoxypropane, 2-(diphenylmethyl)-1,3-dimethoxypropane, 2(1-naphthyl)-1,3-dimethoxypropane, 2(p-fluorophenyl)-1,3-dimethoxypropane, 2(1-decahydronaphthyl)-1,3-dimethoxypropane, 2(p-tert-butylphenyl)-1,3-dimethoxypropane, 2,2-dicyclohexyl-1,3-dimethoxypropane, 2,2-diethyl-1,3-dimethoxypropane, 2,2-dipropyl-1,3-dimethoxypropane, 2,2-dibutyl-1,3-dimethoxypropane, 2,2-diethyl-1,3-diethoxypropane, 2,2-dicyclopentyl-1,3-dimethoxypropane, 2,2-dipropyl-1,3-diethoxypropane, 2,2-dibutyl-1,3-diethoxypropane, 2-methyl-2-ethyl-1,3-dimethoxypropane, 2-methyl-2-propyl-1,3-dimethoxypropane, 2-methyl-2-benzyl-1,3-dimethoxypropane, 2-methyl-2-phenyl-1,3-dimethoxypropane, 2-methyl-2-cyclohexyl-1,3-dimethoxypropane, 2-methyl-2-methylcyclohexyl-1,3-dimethoxypropane, 2,2-bis(p-chlorophenyl)-1,3-dimethoxypropane, 2,2-bis(2-phenylethyl)-1,3-dimethoxypropane, 2,2-bis(2-cyclohexylethyl)-1,3-dimethoxypropane, 2-methyl-2-isobutyl-1,3-dimethoxypropane, 2-methyl-2-(2-ethylhexyl)-1,3-dimethoxypropane, 2,2-bis(2-ethylhexyl)-1,3-dimethoxypropane,2,2-bis(p-methylphenyl)-1,3-dimethoxypropane, 2-methyl-2-isopropyl-1,3-dimethoxypropane, 2,2-diisobutyl-1,3-dimethoxypropane, 2,2-diphenyl-1,3-dimethoxypropane, 2,2-dibenzyl-1,3-dimethoxypropane, 2-isopropyl-2-cyclopentyl-1,3-dimethoxypropane, 2,2-bis(cyclohexylmethyl)-1,3-dimethoxypropane, 2,2-diisobutyl-1,3-diethoxypropane, 2,2-diisobutyl-1,3-dibutoxypropane, 2-isobutyl-2-isopropyl-1,3-dimetoxypropane, 2,2-di-sec-butyl-1,3-dimetoxypropane, 2,2-di-tert-butyl-1,3-dimethoxypropane, 2,2-dineopentyl-1,3-dimethoxypropane, 2-iso-propyl-2-isopentyl-1,3-dimethoxypropane, 2-phenyl-2-benzyl-1,3-dimetoxypropane, 2-cyclohexyl-2-cyclohexylmethyl-1,3-dimethoxypropane.
Specially preferred are the compounds of formula (II):
where the RVI radicals equal or different are hydrogen; halogens, preferably Cl and F; C1–C20 alkyl radicals, linear or branched; C3–C20 cycloalkyl, C6–C20 aryl, C7–C20 alkylaryl and C7–C20 aralkyl radicals, optionally containing one or more heteroatoms selected from the group consisting of N, O, S, P, Si and halogens, in particular Cl and F, as substitutes for carbon or hydrogen atoms, or both; the radicals RIII and RIV are as defined above for formula (I).                Specific examples of compounds comprised in formula (II) are:        9,9-bis(methoxymethyl)fluorene;        9,9-bis(methoxymethyl)-2,3,6,7-tetramethylfluorene;        9,9-bis(methoxymethyl)-2,3,4,5,6,7-hexafluorofluorene;        9,9-bis(methoxymethyl)-2,3-benzofluorene;        9,9-bis(methoxymethyl)-2,3,6,7-dibenzofluorene;        9,9-bis(methoxymethyl)-2,7-diisopropylfluorene;        9,9-bis(methoxymethyl)-1,8-dichlorofluorene;        9,9-bis(methoxymethyl)-2,7-dicyclopentylfluorene;        9,9-bis(methoxymethyl)-1,8-difluorofluorene;        9,9-bis(methoxymethyl)-1,2,3,4-tetrahydrofluorene;        9,9-bis(methoxymethyl)-1,2,3,4,5,6,7,8-octahydrofluorene;        9,9-bis(methoxymethyl)-4-tert-butylfluorene.        9,9-bis(methoxymethyl)fluorene being the most preferred.        
The catalyst systems comprising the solid catalyst components obtained with the process of the present invention are particularly suitable to homo- or co-polymerise α-olefins of formula CH2═CHR, wherein R is hydrogen or an alkyl, cycloalkyl, aryl, arylalkyl or alkylaryl radical with 1 to 12 carbon atoms. A preferred field of application is the stereospecific polymerisation of propylene for the preparation of homopolymer or copolymers thereof.
The diether-based catalyst components described above are generally used after contacting them with an aluminium compound such as an aluminium-trialkyl or an aluminium-alkyl-hydride. A commonly used aluminium compound is triethyl-aluminium.
Particularly when isotactic polymers are produced, an external electron donor can be contacted with the di-ether based catalyst component of the invention. Suitable external electron donor compounds include silicon compounds, ethers, esters, amines, heterocyclic compounds. Preferred compounds used as external donors are silicon compounds containing at least one Si—OR bond (R being a hydrocarbon radical). Among them, particularly preferred are the silicon compounds of formula Ra5Rb6Si(OR7)c, where a and b are integer from 0 to 2, c is an integer from 1 to 3 and the sum (a+b+c) is 4; R5, R6, and R7, are alkyl, cycloalkyl or aryl radicals with 1–18 carbon atoms optionally containing heteroatoms. Particularly preferred are the silicon compounds in which a is 1, b is 1, c is 2, at least one of R5 and R6 is selected from branched alkyl, cycloalkyl or aryl groups with 3–10 carbon atoms optionally containing heteroatoms and R7 is a C1–C10 alkyl group, in particular methyl. Examples of such preferred silicon compounds are methylcyclohexyldimethoxysilane, diisopropyldimethoxysilane, diphenyl-dimethoxysilane, methyl-t-butyldimethoxysilane, dicyclopentyldimethoxysilane, 2-ethylpiperidinyl-2-t-butyldimethoxysilane and 1,1,1,trifluoropropyl-2-ethylpiperi-dinyl-dimethoxysilane. Moreover, are also preferred the silicon compounds in which a is 0, c is 3, R6 is a branched alkyl or cycloalkyl group, optionally containing heteroatoms, and R7 is methyl. Examples of such preferred silicon compounds are cyclohexyltrimethoxysilane, t-butyltrimethoxysilane and thexyltrimethoxysilane.
The external electron donor compound (c) is used in such an amount to give a molar ratio between the organoaluminum compound and said electron donor compound (c) of from 0.1 to 500, preferably from 1 to 300 and more preferably from 3 to 100. As previously indicated, when used in the (co)polymerization of olefins, and in particular of propylene, the catalysts of the invention allow to obtain, with high yields, polymers having a high isotactic index (expressed by high xylene insolubility X.I.), thus showing an excellent balance of properties.
Therefore, it is a further object of the present invention a process for the homo- or copolymerization of olefins CH2═CHR, in which R is hydrogen or a hydrocarbyl radical with 1–12 carbon atoms, carried out in the presence of a catalyst as described above.
Said polymerization process can be carried out according to known techniques for example slurry polymerization using as diluent an inert hydrocarbon solvent, or bulk polymerization using the liquid monomer (for example propylene) as a reaction medium. Moreover, it is possible carrying out the polymerization process in gas-phase operating in one or more fluidized or mechanically agitated bed reactors.
The polymerization is generally carried out at temperature of from 20 to 120° C., preferably of from 40 to 80° C. When the polymerization is carried out in gas-phase the operating pressure is generally between 0.5 and 10 MPa, preferably between 1 and 5 MPa. In the bulk polymerization the operating pressure is generally between 1 and 6 MPa preferably between 1.5 and 4 MPa. Hydrogen or other compounds capable to act as chain transfer agents can be used to control the molecular weight of polymer.
The following examples will further illustrate the present invention without limiting its scope.